1. Field of the Invention
The present invention relates to a freezing prevention system for a refrigeration device such as a vehicle air conditioner. More particularly, the present invention relates to a freezing prevention control for preventing a refrigerant evaporator from freezing.
2. Description of Related Art
A freezing prevention system of a refrigeration device includes an air temperature sensor that is disposed downstream of a refrigerant evaporator in an air flow direction for detecting an air temperature at an air outlet side of the refrigerant evaporator. In the freezing prevention system, a freezing prevention control is performed such that operation of a compressor is stopped when an air temperature detected by the air temperature sensor reduces lower than a predetermined temperature. Generally, even when a surface temperature of the evaporator changes rapidly, the air temperature detected by the air temperature sensor cannot be changed rapidly in accordance with this rapid temperature change of the surface temperature.
To overcome this problem, in a freezing prevention system disclosed in JP-A-2000-258001, an air flow reducing member is disposed to reduce an air flow rate at an outlet side of an evaporator, and a freezing-prevention temperature sensor is disposed in an air flow reducing area of the air flow reducing member. Further, an air flow increasing member is disposed to increase an air flow rate at the outlet side of the evaporator, and a re-start temperature sensor is disposed in an air flow increasing area of the air flow increasing member. In addition, operation of a compressor is controlled based on the detected temperatures of the freezing-prevention temperature sensor and the re-start temperature sensor. However, in the freezing prevention system disclosed in JP-A-2000-258001, when the response performance of the temperature sensors is increased, an operation starting frequency and an operation stopping frequency of the compressor are increased, thereby reducing durability of a solenoid clutch, and worsening drivability and dehumidifying performance. Further, the freezing-prevention temperature sensor, the re-start temperature sensor, the air flow reducing member, the air flow increasing member and the like are required. Therefore, production cost of this freezing prevention system is increased.